Agropyron mosaic virus (AgMV) from Agropyron repens and ryegrass mosaic virus (RyMV) from Lolium perenne L. and Lolium multiflorum Lam. were investigated. Isolates did not react with wheat streak mosaic antisera. Flexuous, filiform virions of both viruses were about 700 nm long. Agropyron repens L. Secale cereale L. and Triticum aestivum L. proved to be susceptible hosts of isolates from Agropyron; Avena sativa L. Hordeum vulgare L. and Zea mays L. were resistant. Isolates originated from Lolium species were able to infect only Avena sativa L. Dactylis glomerata L. Lolium multiflorum Lam. and L. perenne L. Table 1 shows summarized symptoms of AgMV and RyMV isolates in test plants in comparison with Hungarian isolate of wheat streak mosaic virus (WSMV). Both AgMV and RyMV are common in the country. Until now, these two viruses have not been isolated from cereals, though AgMV was potential pathogen of wheats and RyMV of oats alike.